1. Field of the Invention
The present invention relates to a method for producing an improved composite molding compound. More particularly, the invention relates to a method and apparatus of manufacturing an "oriented" composite molding compound utilizing discontinuous fibers which are embedded in a resin matrix for machining and press molding applications.
2. Discussion of the Prior Art
There are currently a number of commercial and defense manufacturing companies that are using composite molding compounds as a low cost alternative to the use of continuous fiber reinforced "prepregs" (sheets of uncured resin impregnated onto continuous reinforcement fibers) for the manufacturing of composite structures in the aerospace and automotive industry. Additionally, it is well known in the manufacturing arts that molding compounds are also much better suited than continuous fiber reinforced prepreg for the fabrication of complex shaped parts.
However, the molding compounds used today are composed of fibers having a random orientation which results in sacrificing a significant level of mechanical strength when compared to reinforced prepregs composed of fibers which are "oriented" in a desired direction. As a result of the random orientation of the fibers which is inherent in commercially available molding compounds, a number of applications which would benefit from the process advantages of molding compounds are not realized due to its sacrifice in mechanical strength.
Therefore, a need exists to provide an inexpensive and reliable method of making a composite molding compound that exhibits the tailorable fiber orientations which lead to significant strength improvements. Furthermore, a need exists to provide a composite molding compound which can be either machined or inserted within a molding die, compressed and hardened to form a high strength shaped member.
The subject invention herein solves all of these problems in a new and unique manner which has not been part of the art previously. Some related patents are described below:
U.S. Pat. No. 5,158,824 issued to F. Gill et al. on Oct. 27, 1992.
This patent describes a wet mat process for producing a non-woven fibrous mat of generally random fiber orientation. The non-woven fibrous mat comprises built-up lines or strips of fiber directionally formed to enhance the strength and/or appearance of the mat. The wet mat process utilizes a continuous traveling forming belt which controls the thickness and orientations of the fibers by controlling the flow of the fiber material onto the forming belt by a vacuum technique.
U.S. Pat. No. 4,271,112 issued to F. Rossman on Jun. 2, 1981
This patent is directed to a process for producing a high strength, rotationally symmetrical component by appending short fibers of glass, carbon or like material in an organic solvent, and depositing the fiber material in a rotating sieve-like receptacle through a radially movable nozzle. The produced pre-form is impregnated with a matrix of resin and hardener and pressed into its final shape.
U.S. Pat. No. 5,196,212 issued to G. M. Knoblach on Mar. 23, 1993
This patent describes an apparatus for the production of composite material parts by aligning reinforcing fibers through application of electric fields. The fibers are in the form of rods, pre-impregnated with a matrix material or coated with a sizing, and aligned within a dielectric alignment fluid. The apparatus utilizes electrodes whose location creates an electric field thereby mimicking the stress lines exhibited by the final composite part when under stress. By use of the flux lines of the electric field, the reinforcing fibers are aligned in accordance with predetermined stress lines.
U.S. Pat No. 5,198,167 issued to T. Ohta et al. on Mar. 30, 1993
This patent is directed to a process for molding a fiber reinforced composite material with short fibers oriented in one direction. The process utilizes a slurry molding material having short fibers disbursed in a liquid and further uses pressing forces which are applied to the molding material from two directions substantially perpendicular to each other within the mold while simultaneously removing the liquid.
While the basic concepts presented in the aforesaid patents are desirable, the method and apparatus employed by each to produce a molding compound with oriented fibers are far too complicated to render them as an inexpensive means of achieving a reinforced polymer matrix composite having superior mechanical properties.